Item: FROM PUBLICLY AVAILABLE WEBCAMS TO ICE-AVALANCHE HAZARD ASSESSMENT: A DECADE OF SERAC FALLS FROM A HANGING GLACIER OF THE MONT-BLANC MASSIF (FRANCE)
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Title: FROM PUBLICLY AVAILABLE WEBCAMS TO ICE-AVALANCHE HAZARD ASSESSMENT: A DECADE OF SERAC FALLS FROM A HANGING GLACIER OF THE MONT-BLANC MASSIF (FRANCE)
Proceedings: Proceedings, International Snow Science Workshop, Whistler, BC, Canada, 2026
Authors:
- Grégoire Guillet [ Avalanche Research Program, Simon Fraser University, Burnaby, BC, Canada ] [ Department of Geosciences, University of Oslo, Oslo, Norway ]
- Ludovic Ravanel [ EDYTEM, University Savoie Mont-Blanc, CNRS (UMR 5204), Le Bourget du Lac, France ] [ Avalanche Research Program, Simon Fraser University, Burnaby, BC, Canada ]
Date: 2026-09-28
Abstract: Outside a few studies of ice masses threatening valleys (e.g., Weissmies, Taconnaz, and Grandes Jorasses in the Alps), hanging glaciers (HGs) and their dynamics remain poorly understood. Because individual collapses are rarely observed and measured, the size and frequency of serac falls remain largely unquantified. We use the Contamine-Négri HG, on the north-eastern side of Mont Blanc du Tacul (4248 m a.s.l., Mont-Blanc massif, France), as a case study. Repeated serac falls from this HG trigger ice avalanches across heavily travelled mountaineering routes. Recent near-fatal events include 22 May 2020, when ~15,000 m³ of ice partially rebounded nearly 50 m up the north face of Pointe Lachenal, and 8 May 2025, when >60,000 m³ generated two avalanches (450 m northwards, burying three people, and 700 m eastwards). We analyzed a decade (2016–2026) of daily imagery from two webcams successively installed at the Aiguille du Midi (3842 m a.s.l.), 1.7 km from the HG. Using single-image photogrammetry with a Bayesian model, we estimated the volume of each major collapse. For every resolvable event, we measured the released ice surface area and volume, building a decade-long catalogue and magnitude-frequency distribution. Repurposing publicly available webcam archives as calibrated, georeferenced measurements transforms tourism infrastructure into a quantitative tool for studying serac falls and ice avalanches. The resulting magnitude-frequency distribution and seasonal release rates provide return periods and time-varying exposure probabilities, supporting seasonal guidance and future assessment of climate-driven changes. Peak activity coincides with route use, mainly from late spring to late autumn.
Object ID: ISSW2026_P3.61.pdf
DOI: https://doi.org/10.15788/1790099244
Language of Article: English
Presenter(s): Gregoire Guillet
Keywords: Ice avalanches, serac falls, hanging glacier, Bayesian inference, Mont Blanc du Tacul.
Page Number(s): 2491 - 2498
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